SIRT1 decreases Lox-1-mediated foam cell formation in atherogenesis

AIMS

Endothelial activation, macrophage infiltration, and foam cell formation are pivotal steps in atherogenesis. Our aim in this study was to analyse the role of SIRT1, a class III deacetylase with important metabolic functions, in plaque macrophages and atherogenesis.

METHODS AND RESULTS

Using partial SIRT1 deletion in atherosclerotic mice, we demonstrate that SIRT1 protects against atherosclerosis by reducing macrophage foam cell formation. Peritoneal macrophages from heterozygous SIRT1 mice accumulate more oxidized low-density lipoprotein (oxLDL), thereby promoting foam cell formation. Bone marrow-restricted SIRT1 deletion confirmed that SIRT1 function in macrophages is sufficient to decrease atherogenesis. Moreover, we show that SIRT1 reduces the uptake of oxLDL by diminishing the expression of lectin-like oxLDL receptor-1 (Lox-1) via suppression of the NF-κB signalling pathway.

CONCLUSION

Our findings demonstrate protective effects of SIRT1 in atherogenesis and suggest pharmacological SIRT1 activation as a novel anti-atherosclerotic strategy by reducing macrophage foam cell formation.

Endothelial-vasoprotective effects of high-density lipoprotein are impaired in patients with type 2 diabetes mellitus but are improved after extended-release niacin therapy

BACKGROUND

High-density lipoprotein (HDL)-raising therapies are currently under intense evaluation, but the effects of HDL may be highly heterogeneous. We therefore compared the endothelial effects of HDL from healthy subjects and from patients with type 2 diabetes mellitus and low HDL (meeting the criteria for metabolic syndrome), who are frequently considered for HDL-raising therapies. Moreover, in diabetic patients, we examined the impact of extended-release (ER) niacin therapy on the endothelial effects of HDL.

METHODS AND RESULTS

HDL was isolated from healthy subjects (n=10) and patients with type 2 diabetes (n=33) by sequential ultracentrifugation. Effects of HDL on endothelial nitric oxide and superoxide production were characterized by electron spin resonance spectroscopy analysis. Effects of HDL on endothelium-dependent vasodilation and early endothelial progenitor cell-mediated endothelial repair were examined. Patients with diabetes were randomized to a 3-month therapy with ER niacin (1500 mg/d) or placebo, and endothelial effects of HDL were characterized. HDL from healthy subjects stimulated endothelial nitric oxide production, reduced endothelial oxidant stress, and improved endothelium-dependent vasodilation and early endothelial progenitor cell-mediated endothelial repair. In contrast, these beneficial endothelial effects of HDL were not observed in HDL from diabetic patients, which suggests markedly impaired endothelial-protective properties of HDL. ER niacin therapy improved the capacity of HDL to stimulate endothelial nitric oxide, to reduce superoxide production, and to promote endothelial progenitor cell-mediated endothelial repair. Further measurements suggested increased lipid oxidation of HDL in diabetic patients, and a reduction after ER niacin therapy.

CONCLUSIONS

HDL from patients with type 2 diabetes mellitus and metabolic syndrome has substantially impaired endothelial-protective effects compared with HDL from healthy subjects. ER niacin therapy not only increases HDL plasma levels but markedly improves endothelial-protective functions of HDL in these patients, which is potentially more important.

CLINICAL TRIAL REGISTRATION

clinicaltrials.gov. Identifier: NCT00346970.

Vascular abnormalities, paraoxonase activity, and dysfunctional HDL in primary antiphospholipid syndrome

CONTEXT

Accelerated atherosclerosis has been described in antiphospholipid syndrome, but the vascular abnormalities and the underlying mechanisms remain unclear.

OBJECTIVES

To compare vascular structure and function in patients with positive antiphospholipid antibodies (aPL) with controls and to assess their relationship with paraoxonase activity.

DESIGN, SETTING, AND PARTICIPANTS

A cross-sectional study of 77 women with positive antiphospholipid antibodies from a lupus outpatient clinic in London, England (90% of the eligible population) and 77 controls matched on frequency basis for age and cardiovascular risk factors between June 2006 and April 2009. Carotid intima media thickness (CIMT), flow-mediated dilatation, pulse wave velocity, and paraoxonase activity were measured in all patients. Anti-inflammatory and antioxidant properties of high-density lipoprotein (HDL) were examined.

MAIN OUTCOME MEASURES

CIMT, pulse wave velocity, flow-mediated dilatation, and paraoxonase.

RESULTS

Women with aPL had greater CIMT and pulse wave velocity compared with controls (mean [SD], 0.75 [0.16] vs 0.64 [0.09] mm; 95% confidence interval [CI], -0.14 to -0.06; P < .001; and 9.2 [1.6] vs 8.5 [1.8] m/s; 95% CI, -1.14 to -0.06; P = .04) and lower flow-mediated dilatation (6.2% [4.1%] vs 9.6% [4.2%]; 95% CI, 2.02%-4.69%; P < .001). Paraoxonase activity was lower in women with aPL vs controls (median [interquartile range], 91.2 [64.3-105.1] vs 103.0 [80.5-111.5] micromol p-nitrophenol/L/serum/min; 95% CI, 0.004-0.007; P = .005) and was inversely associated with CIMT and pulse wave velocity in women with aPL (standardized beta coefficient = -0.4 and -0.3, respectively; P < .05 for both), but not in the control group. High-density lipoprotein from women with aPL inhibited endothelial nitric oxide production in human aortic endothelial cells, in contrast with controls. The beneficial effects of HDL from women with aPL on vascular cell adhesion molecule 1 expression, superoxide production, and monocyte adhesion following activation of human aortic endothelial cells were largely blunted.

CONCLUSIONS

Compared with controls, women with aPL had greater functional and structural arterial abnormalities, which were associated with lower activity of paraoxonase. In patients with aPL, HDL reduced nitric oxide bioavailability and had impaired anti-inflammatory and antioxidant properties.

Pharmacological approaches to improve endothelial repair mechanisms

Endothelial injury is thought to play a pivotal role in the development and progression of vascular diseases, such as atherosclerosis, hypertension or restenosis, as well as their complications, including myocardial infarction or stroke. Accumulating evidence suggests that bone marrow-derived endothelial progenitor cells (EPCs) promote endothelial repair and contribute to ischemia-induced neovascularization. Coronary artery disease and its risk factors, such as diabetes, hypercholesterolemia, hypertension and smoking, are associated with a reduced number and impaired functional activity of circulating EPCs. Moreover, initial data suggest that reduced EPC levels are associated with endothelial dysfunction and an increased risk of cardiovascular events, compatible with the concept that impaired EPC-mediated vascular repair promotes progression of vascular disease. In this review we summarize recent data on the effects of pharmacological agents on mobilization and functional activity of EPCs. In particular, several experimental and clinical studies have suggested that statins, angiotensin-converting enzyme inhibitors, angiotensin II type 1 receptor blockers, PPAR-gamma agonists and erythropoietin increase the number and functional activity of EPCs. The underlying mechanisms remain largely to be defined; however, they likely include activation of the PI3-kinase/Akt pathway and endothelial nitric oxide synthase, as well as inhibition of NAD(P)H oxidase activity of progenitor cells.

Oxidant stress impairs in vivo reendothelialization capacity of endothelial progenitor cells from patients with type 2 diabetes mellitus: restoration by the peroxisome proliferator-activated receptor-gamma agonist rosiglitazone

BACKGROUND

Endothelial progenitor cells (EPCs) are thought to contribute to endothelial recovery after arterial injury. We therefore compared in vivo reendothelialization capacity of EPCs derived from patients with diabetes mellitus and healthy subjects. Moreover, we examined the effect of treatment with the peroxisome proliferator-activated receptor-gamma agonist rosiglitazone on oxidant stress, nitric oxide (NO) bioavailability, and the in vivo reendothelialization capacity of EPCs from diabetic individuals.

METHODS AND RESULTS

In vivo reendothelialization capacity of EPCs from diabetic patients (n=30) and healthy subjects (n=10) was examined in a nude mouse carotid injury model. Superoxide and NO production of EPCs was determined by electron spin resonance spectroscopy. Thirty patients with diabetes mellitus were randomized to 2 weeks of rosiglitazone (4 mg BID p.o.) or placebo treatment. In vivo reendothelialization capacity of EPCs derived from diabetic subjects was severely reduced compared with EPCs from healthy subjects (reendothelialized area: 8+/-3% versus 37+/-10%; P<0.001). EPCs from diabetic individuals had a substantially increased superoxide production and impaired NO bioavailability. Small-interfering RNA silencing of NAD(P)H oxidase subunit p47(phox) reduced superoxide production and restored NO bioavailability and in vivo reendothelialization capacity of EPCs from diabetic patients. Importantly, rosiglitazone therapy normalized NAD(P)H oxidase activity, restored NO bioavailability, and improved in vivo reendothelialization capacity of EPCs from diabetic patients (reendothelialized area: placebo versus rosiglitazone, 8+/-1% versus 38+/-5%; P<0.001).

CONCLUSIONS

In vivo reendothelialization capacity of EPCs derived from individuals with diabetes mellitus is severely impaired at least partially as a result of increased NAD(P)H oxidase-dependent superoxide production and subsequently reduced NO bioavailability. Rosiglitazone therapy reduces NAD(P)H oxidase activity and improves reendothelialization capacity of EPCs from diabetic individuals, representing a potential novel mechanism whereby peroxisome proliferator-activated receptor-gamma agonism promotes vascular repair.